This invention relates in general to a method and apparatus for balancing an article, such a vehicular driveshaft tube or driveshaft assembly, for rotation about an axis. More specifically, this invention relates an improved method and apparatus for automatically balancing such an article by initially mounting an annular balance ring thereon, securing certain portions of the balance ring to the article, and removing the remaining portions thereof so as to automatically balance the article.
In most land vehicles, a source of rotational energy, such as an internal combustion or diesel engine, is connected by means of a driveshaft assembly to rotate one or more driven wheels. The driveshaft assembly typically extends between an output shaft of a transmission, which is connected to and rotatably driven by the engine, and an input shaft of an axle assembly, or transfer case which is connected to rotatably drive the driven wheels. In some vehicles, the distance separating the transmission and the axle assembly is relatively short. In these vehicles, the driveshaft assembly can be formed from a single driveshaft tube having first and second universal joints that connect the ends of the driveshaft tube to the output shaft of the transmission and the input shaft of the axle assembly. In other vehicles, the distance separating the transmission and the axle assembly is relatively long, making the use of a single driveshaft tube impractical. In these vehicles, the driveshaft assembly can be formed from a plurality of separate driveshaft tubes. The driveshaft tubes are connected together by a first universal joint, and second and third universal joints are provided to connect the ends of the driveshaft tubes to the output shaft of the transmission and the input shaft of the axle assembly.
Ideally, each of the driveshaft tubes would be formed in the shape of a cylinder that is absolutely round, absolutely straight, and has an absolutely uniform wall thickness. Such a perfectly shaped driveshaft tube would be precisely balanced for rotation and, therefore, would not generate any undesirable noise or vibration during use. In actual practice, however, the driveshaft tubes usually contain variations in roundness, straightness, and wall thickness that result in minor imbalances when rotated at high speeds. To prevent such imbalances from generating undesirable noise or vibration when rotated during use, therefore, it is commonplace to counteract such imbalances by securing balance weights to selected portions of the driveshaft tube. The balance weights are sized and positioned to counterbalance the imbalances of the driveshaft tube such that it is balanced for rotation during use.
Traditionally, the balancing process has been performed through the use of a conventional balancing machine. The balancing machine includes a pair of fittings that are adapted to support the ends of the driveshaft assembly thereon. The balancing machine further includes a motor for rotating the driveshaft assembly at a predetermined speed. As the driveshaft assembly is rotated, the balancing machine senses vibrations that are caused by imbalances in the structure of the driveshaft assembly. The balancing machine is responsive to such vibrations for determining the size and location of one or more balance weights that, if secured to the driveshaft, will minimize these imbalances. The rotation of the driveshaft assembly is then stopped to allow such balance weights to be secured to the outer surface of the driveshaft assembly in a conventional manner, such as by welding, adhesives, and the like. The driveshaft assembly is again rotated to confirm whether proper balance has been achieved or to determine if additional balance weights are required. A number of such balancing machines of this general structure and method of operation are known in the art.
Although such prior art balancing machines have been effective, this balancing process has been found to be relatively slow and inefficient. This is because each driveshaft tube must usually be rotated and measured at least two times, a first time to measure the imbalances and determine the size and location of the balance weights, and a second time to confirm that proper balance has been achieved after the balance weights have been secured thereto. This time consuming process is particularly problematic in the context of balancing vehicular driveshaft tube, which are typically manufactured in relatively large volumes. Thus, it would be desirable to provide an improved method and apparatus for quickly and efficiently balancing an article, such a tube for use in a vehicular driveshaft assembly, for rotation about an axis.
This invention relates to an improved method and apparatus for quickly and balancing an article, such as a tube for use in a vehicular driveshaft assembly, for rotation about an axis. Initially, a balance ring is press fit or otherwise mounted onto the article to be balance . The balance ring includes a ring of a material that can be selectively removed to balance the article for rotation, such as powdered metal. The article is mounted on an apparatus for rotating the article at a predetermined speed and for sensing vibrations that are caused by imbalances in the structure of the article. An electronic controller is responsive to such sensed vibrations for determining the size and location of one or more balance weights that, if secured to the article, will minimize or eliminate these imbalances. The electronic controller actuates a source of energy to alter the physical properties (such as by hardening, for example) of only those portions of the ring that correspond with the size and location of the balance weights that will minimize or eliminate the imbalances therein. Thereafter, the unhardened portions of the ring are removed, leaving only the hardened portions thereof as the balance weights.